Method for controlling speed and/or distance in motor vehicles

ABSTRACT

The invention relates to a method for controlling speed and/or distance in motor vehicles having distance-related longitudinal control systems, wherein during clear driving, a clear drive acceleration value is set to reach a preset speed, and while following a detected target object, a following acceleration value is set to maintain a preset distance from the target object, and wherein if the target object is lost during a following drive operation, a transition acceleration value is set. According to the invention, the transition acceleration value is set for the duration of a time interval, which is dependent on the speed at the time of the target object loss.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date under 35 U.S.C.§119(a)-(d) of International Patent Application No.: PCT/EP2007/009873filed Nov. 15, 2007, which claims the priority of German PatentApplication No. DE 10 2006 056 629.7 filed on Nov. 30, 2006.

FIELD OF THE INVENTION

The invention relates to a method for controlling speed and/or distancein motor vehicles having distance-related longitudinal control systems.

BACKGROUND

Motor vehicles having longitudinal control systems are well known. Mostof the currently available longitudinal control systems control thespeed of the motor vehicle by setting an acceleration value at a presetdesired or theoretical speed. Additionally, longitudinal control systemsenhanced by distance control, which are known as distance-relatedlongitudinal control systems, are also obtainable today from somemanufacturers. Such systems, offered, for example by BMW, the Assigneeof the present invention, under the name of “Active Cruise Control”,make it possible to automatically drive the motor vehicle whilemaintaining a desired distance from the vehicle ahead, at a desiredspeed or at an appropriately slower speed. In principle, the generallyknown longitudinal control or vehicle speed control systems, whichmaintain a specific predetermined speed, are enhanced by an additionaldistance function, such that the use of an “active” driving speedcontrol of this type is also possible in heavy motorway and non-motorwayroad traffic. The system is therefore generally able to adjust thevehicle's speed to suit the surrounding traffic conditions.

The Active Cruise Control System maintains a desired or set speed whenthe driver's lane is clear. Under the clear lane condition, a cleardrive acceleration value is set. A distance sensor system on the motorvehicle, operating, for example, with a radar, detects a target objector vehicle ahead in the host vehicle's lane. The speed of the hostvehicle is adjusted, by the system, to the speed of the motor vehicle ortarget object ahead, for example, by initiating a suitable followingacceleration value, such that a distance control contained in the ActiveCruise Control System or in the corresponding longitudinal controlsystem automatically maintains a preset distance, appropriate for thesituation, from the motor vehicle or target object ahead.Distance-controlled longitudinal control systems of this type aregenerally only active or operable beyond a minimum speed of, for example30 km/h. However, these systems can be enhanced by a “stop-and-gofunction”, such that distance-related longitudinal control is possibleup to and out of standstill.

If, during the control process, at a preset distance from a targetobject ahead at relatively high speeds, the loss of a target object isdetected, the distance-related longitudinal control systems aregenerally configured such that they immediately switch over from followcontrol operation into clear drive control (i.e. into the control madefor reaching the preset speed). However, this is a problem when thedetected loss of the target object is only temporary, because the targetobject ahead is travelling around a bend, or the loss of the targetobject is detected due to a sensor error.

DE 100 47 746 A1 discloses a method for distance-related longitudinalcontrol in which, following the loss of a target object and using theinformation of a navigation system, a probability of the vehicle ortarget object ahead and/or of the host motor vehicle travelling around abend is determined. If the determined probability exceeds apredetermined threshold, a time-delayed clear drive acceleration to thepreset speed is carried out.

DE 100 06 403 A1 discloses a method for controlling speed and distancein which, and in the event of losing a target object, a transitionacceleration value is calculated. Therefore, the vehicle's speed wouldbe a function of the speed of the target object before it was lost, ofthe driving speed of the motor vehicle and of the distance from theoriginal target object until a new target object is detected.Additionally, the vehicle's speed could be a function until the motorvehicle has reached the location where the target object was lost. Fromthis time, either the usual control following the new target objectstarts or a clear drive control starts.

A problem exists in reproducing controllable vehicle behaviour when atarget object has been detected as being lost at low speeds(stop-and-go) and with resulting very short distances from the originaltarget objects. Attempts to address this problem, in the event of theloss of a target object at very low speeds, for example below 30 km/h,have the entire distance-related longitudinal control system switchedoff.

SUMMARY

An object of the invention, among others, is to provide an improvedmethod, which is particularly suitable for use in stop-and-go operation,for controlling speed and distance when a loss of a target object isdetected. This and other objectives are achieved through a method forcontrolling speed and/or distance in motor vehicles havingdistance-related longitudinal control systems, wherein during cleardriving, a clear drive acceleration value is set for reaching a presetspeed, and during driving following a detected target object, a followdrive acceleration value is set for maintaining a preset distance fromthe target object, and wherein if the target object is lost duringfollow drive operation, a transition acceleration value is set, whereinthe transition acceleration value is set for the duration of a timeinterval which is dependent on the speed at the time of the targetobject loss.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in detail with reference to anembodiment.

FIG. 1 shows a probability of a target object loss determined andplotted over time, within a speed-dependent time interval; and

FIG. 2 shows a transition acceleration value set as a function of theprobability of the target object loss, within the speed-dependent timeinterval.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

FIG. 1 shows a diagram in which the determined target object lossprobability WK is plotted over the time t. The target object lossprobability WK indicates the likelihood that a target object is actuallyno longer in front of the motor vehicle.

From the start of the time t until a time t1, using suitable sensors, atarget object is detected and denoted in this case by ZO+. Within thistime range, the target object loss probability WK is 0, since no targetobject loss has been detected. As long as the target object is detected,no target object loss probability WK is determined.

At time t1, the loss of the target object is detected, denoted here byZO−. As a function of the actual speed of the motor vehicle, at the timet1 of the target object loss, a time interval from t1 to t2 is then set,within which the target object loss probability WK is determined. At thestart of the detected target object loss period ZO−, i.e. shortly afterthe time t1, it is assumed that the loss is just based on incorrectinformation, for example on a defective sensor signal. Thus, the targetobject loss probability WK is zero 0 or almost zero 0.

As time t passes, from the start of the detected target object lossperiod ZO−, the target object probability WK increases. If, up to thespeed-dependent time t2, no target object is (again) detected, thetarget object loss probability WK increases continuously until itassumes the value 1 by time t2. The target object loss probability WKincreases as a function of the time t, in that, at t1 of target objectloss, the target object loss probability WK increases from 0 to 1. Theslope of this function is derived from the speed of the motor vehicle atthe time t1 of the target object loss, as this is the basis for thelength of the time interval from t1 to t2.

FIG. 2 shows the acceleration a of the motor vehicle for the variousmodes of the distance-related longitudinal control system described. Forpurposes of simplification, all the acceleration values are assumed tobe constant. As long as the motor vehicle is in a following driveoperation, i.e. a target object is detected, for longitudinal control, afollowing drive acceleration value a_ZO+ is set for reaching ormaintaining a preset distance from a vehicle ahead. If a target objectloss is then detected at time t1, the control, maintaining the setdistance, is interrupted. The distance-related longitudinal controlsystem then determines a clear drive acceleration value a_ZO−, whichwould be set to reach the preset speed if the distance-relatedlongitudinal control system had only been activated at time t1 and therewas no target object in front of the motor vehicle. Furthermore, a startacceleration value a_St is determined or set which can be dependent onvarious parameters or operating conditions of the motor vehicle,preferably on the speed of the motor vehicle at the time of the targetobject loss. The start acceleration value can be recorded, for examplein a performance map.

The distance-related longitudinal control system then determines withinthe speed-dependent time interval from t1 to t2 a transitionacceleration value a_Ü, which is set for longitudinal control withinthis time interval from t1 to t2. The transition acceleration value a_Üis determined within the time interval from t1 to t2, as a function ofthe determined target object loss probability WK from FIG. 1. Theinterrelationship between the transition acceleration value a_Ü and thetarget object loss probability WK can be described by the followingequation:a _(—) Ü=a _(—) St+WK*(a _(—) ZO−−a _(—) St)

As mentioned above, a_ZO− is a clear drive acceleration value whichwould be set for the control if the distance-related longitudinalcontrol system had been activated at the time t1 and at the same speed.The start acceleration value a_St, may assume, as a value, either thefollowing acceleration value a_ZO+ or a value between the followingacceleration value a_ZO+ and the clear drive acceleration value a_ZO−.

Thus, a transition acceleration value a_Ü is produced within thespeed-dependent time interval from t1 to t2, such that the valueincreases continuously from the start acceleration value a_St until theclear drive acceleration value a_ZO− is reached at time t2. As soon asthe time t2 has been reached, a conventional longitudinal controloperation is performed by setting the clear drive acceleration valuea_ZO−, until a target object is again detected.

Alternatively, for a predetermined time, the transition accelerationvalue a_Ü can also correspond to the start acceleration value a_St, andonly then can the continuous transition take place from the startacceleration value a_St to the clear drive acceleration value a_ZO−.

Therefore, the invention proceeds from the fact that in the event ofclear drive operation, i.e. during a drive when no target object isdetected, the distance-related longitudinal control system sets a cleardrive acceleration value for reaching or maintaining a preset speed. Ifa vehicle ahead, detected as a target object, is located in front of themotor vehicle, i.e. the motor vehicle is in a following situation, afollow drive acceleration value is set to reach or maintain a presetdistance from the target object. The term “acceleration value” can beunderstood to mean positive or negative accelerations in each case.

If during following drive operation, the loss of the target object isdetected, a transition acceleration value is set. According to theinvention the transition acceleration value is determined for theduration of a time interval which is dependent on the speed at the timeof the loss of the target object. In this respect, the longer the timeinterval within certain limits the slower the speed at the time of theloss of the target object. If, within the speed-dependent time interval,a target object is again detected, the determined follow driveacceleration value is again immediately set. Accordingly, at the end ofthe time interval, the clear drive acceleration value is set in a knownmanner, as long as a target object is not detected.

The invention proceeds from the fact that in the event of clear driveoperation, i.e. during a drive when no target object is detected, thedistance-related longitudinal control system sets a clear driveacceleration value a_ZO− for reaching or maintaining a preset speed. Ifa vehicle ahead, detected as a target object, is located in front of themotor vehicle, i.e. the motor vehicle is in a following situation, afollow drive acceleration value a_ZO+ is set to reach or maintain apreset distance from the target object. The term “acceleration value”can be understood to mean positive or negative accelerations in eachcase.

If during following drive operation, the loss of the target object isdetected at t1, a transition acceleration value a_Ü is set. Theinvention provides that the transition acceleration value a_Ü isdetermined for the duration of a time interval (time interval from t1 tot2), which is dependent on the speed at the time of the loss of thetarget object. In this respect, the longer the time interval (timeinterval from t1 to t2), within certain limits, the slower the speed atthe time of target object loss. If, within the speed-dependent timeinterval, a target object is again detected, the determined follow driveacceleration value a_ZO+ is again immediately set. Accordingly, at theend of the time interval, the clear drive acceleration value a_ZO− isset in a known manner, as long as a target object is not detected.

If, during stop-and-go operation, the motor vehicle is in follow controltype of operation, the distance from the vehicle ahead is usually veryshort. If a loss of target object is then detected, for example due to asensor error, although the target object is still there, immediateacceleration of the motor vehicle with a clear drive acceleration valuea_ZO− would result in a very rapid approach to the vehicle ahead. In theworst case scenario, a collision with the target object ahead wouldoccur. The invention affords the advantage that a transitionacceleration value a_Ü can be determined and set even at low speeds fora relatively long time. Thus, the use of the method is particularlyadvantageous at low speeds, which occur in stop-and-go traffic.

The transition acceleration value a_Ü is advantageously determined andset within the time interval (time interval from t1 to t2) as a functionof the time (duration) after the loss of the target object and of thedifference between the clear drive acceleration value a_ZO− and a startacceleration value a_St. The clear drive acceleration value a_ZO− is theacceleration value which would be determined or set if, for example thedesired speed were increased or if the distance-related longitudinalcontrol system had only been activated at this time and at this speed.The start acceleration value a_St can be the following driveacceleration value a_ZO+, which was last determined, or a transitionacceleration value a_Ü that is between the following acceleration valuea_ZO+ and the clear drive acceleration value a_ZO−, and can be dependenton the vehicle speed at the time of the loss of the target object (t1).

In one embodiment of the invention, the transition acceleration valuea_Ü is determined or set as a function of the time (duration) after theloss of the target object, such that the transition acceleration valuea_Ü changes continuously within the speed-dependent time intervalfunction from a start acceleration value a_St to the clear driveacceleration value a_ZO−. The transition acceleration value a_Ü thenincreases over time continuously from the start acceleration value a_Stto the clear drive acceleration value a_ZO−, at the end of thespeed-dependent time interval.

In another embodiment of the invention, the transition accelerationvalue a_Ü can also be determined as a function of the time (duration)after the loss of the target object, such that for a predetermined timeafter the loss of the target object, a start acceleration value a_St isset and then the transition acceleration value a_Ü is changedcontinuously during the time interval. (after the start accelerationvalue has been set up) to the end of the time interval, according to aramp from the start acceleration value a_St to the clear driveacceleration value a_ZO−. This embodiment differs from the previousembodiment only in that the transition acceleration value a_Ücorresponds for a predetermined time to the start acceleration valuea_St, and only then does the start acceleration value a_St adapt to theclear drive acceleration value a_ZO−.

As a function of the time (duration) after the loss of the target objectand the actual speed, a target object loss probability WK canadvantageously also be determined, which increases as the time intervalbetween the time of the loss of the target object and the actual timeafter the loss of the target loss increases, notably if no target objectis present. In this respect, the target object loss probability WK is anindication of the probability of the target object no longer actuallybeing present because, for example it has turned, veered around a bend,or has changed lane. A probability, indicating the likelihood that atarget object is still present, can also be determined, although theloss of the target object has been detected. This probability would thusbe the reciprocal of the target object loss probability WK.

The transition acceleration theoretical value a_Ü can then bedetermined, while incorporating the target object loss probability WKthat has been determined, by multiplying the target object lossprobability WK with the difference between the start acceleration valuea_St and the clear drive acceleration value a_ZO−, and by subsequentlyadding with the start acceleration value a_St. This sets a transitionacceleration value a_Ü, which is optimum in respect of a possiblemeasuring error.

The foregoing illustrates some of the possibilities for practicing theinvention. Many other embodiments are possible within the scope andspirit of the invention. It is, therefore, intended that the foregoingdescription be regarded as illustrative rather than limiting, and thatthe scope of the invention is given by the appended claims together withtheir full range of equivalents.

1. A method for controlling speed or distance or both speed and distancein motor vehicles having a distance-related longitudinal control system,comprising the steps of: setting a clear drive acceleration value withthe distance-related longitudinal control systems for reaching a presetspeed during clear driving; setting a follow drive acceleration valuewith the distance-related longitudinal control systems for maintaining apreset distance from a target object during follow drive operation ofthe target object; setting a transition acceleration value with thedistance-related longitudinal control systems if the target object islost during follow drive operation; determining a target object lossprobability through a microprocessor, the probability being a functionof time after the target object loss and actual speed at a time of thetarget object loss; wherein the transition acceleration value is set fora duration of a time interval and is dependent on a speed at the time ofthe target object loss.
 2. The method according to claim 1, wherein thetime interval is longer, the slower the speed at the time of the targetobject loss.
 3. The method according to claim 2, wherein the transitionacceleration value is set as a function of the time after the targetobject loss and the difference between the clear drive accelerationvalue and a start acceleration value.
 4. The method according to claim3, wherein the transition acceleration value is determined as a functionof the time after the target object loss such that the transitionacceleration value changes continuously within the time interval,according to a ramp function from a start acceleration value to theclear drive acceleration value.
 5. The method according to claim 4,wherein the start acceleration value is the follow drive accelerationvalue or an intermediate acceleration value between the follow driveacceleration value and the clear drive acceleration value.
 6. The methodaccording to claim 3, wherein the transition acceleration value isdetermined as a function of the time after the target object loss suchthat the transition acceleration value corresponds for a predeterminedtime to a start acceleration value and the transition acceleration valuethen changes continuously up to the end of the speed-dependent timeinterval according to a ramp function from the start acceleration valueto the clear drive acceleration value.
 7. The method according to claim6, wherein the start acceleration value is the follow drive accelerationvalue or an intermediate acceleration value between the follow driveacceleration value and the clear drive acceleration value.
 8. The methodaccording to claim 1, wherein the transition acceleration value isdetermined as a function of the time after the target object loss suchthat the transition acceleration value corresponds for a predeterminedtime to a start acceleration value and the transition acceleration valuethen changes continuously up to the end of the speed-dependent timeinterval according to a ramp function from the start acceleration valueto the clear drive acceleration value.
 9. The method according to claim8, wherein the start acceleration value is the follow drive accelerationvalue or an intermediate acceleration value between the follow driveacceleration value and the clear drive acceleration value.
 10. Themethod according to claim 1, wherein the probability advantageouslyincreases as the time interval increases between a time of the targetobject loss and an actual time after the target object loss.
 11. Themethod according to claim 10, wherein the transition acceleration valueis determined by adding the start acceleration value to a value formedby multiplying the target object loss probability with the differencebetween a start acceleration value and the clear drive accelerationvalue.
 12. The method according to claim 1, wherein a transitionacceleration theoretical value is formed as a function of the targetobject loss probability.
 13. The method according to claim 1, whereinthe transition acceleration value is determined by adding a startacceleration value to a value formed by multiplying the target objectloss probability with the difference between the start accelerationvalue and the clear drive acceleration value.